Constant potential apparatus



April 29, 1930. V. BUSH Filed Oot 5I 1925 Patented Apr. 29, 1930 lUNITEDSTATES VANNEVAR BUSH, OF WEST MEDFORD, MASSACHUSETTS, ASSIGNOR T0RAYTHEON,`

PATENT OFFHE CONSTANT-POTENTIAL APPARATUS Application led October 5,1925. Serial No. 60,502.

This invention relates to the art of smoothing pulsating potentials,tha-t is, converting alternating current into uni-directional current ofsubstantially constant potential o r removing the ripples from pulsatingunldirectional current. A typical use of the 1nventi'on is for supplyingsubstantially constant potential current of the order of .one orV twoamperes to the filament of an audion, at six t0 eight volts for example,from an alternating current circuit of customary voltage such as 110volts.

The invention involves the use of a conducting device having acharacteristic curve at least a portion of which is approximatelystraight and parallel with one of its axes, specih'cally the currentabscissa. The device is connected in parallel with the load circuit (e.g. the filament of an audion) and maintains the load voltage constantthroughout the range represented by the horizontal portion of the curveby virtue of the fact that, throughout said range, the voltage acrossits terminals (and therefore across the parallel load circuit) remainssubstantially constant, only the current through the device varying withthe variations in the applied electromotive force. In devices whosecharacteristic curves have only approximately horizontal portions,auxiliary devices, such as chock coils and/or condensers and/orresistances may be employed to assist the smoothing action according towell-known practices.

So far as I am at present aware, the best device having a substantiallyhorizontal characteristic curve is that disclosed in the application ofCharles Gr. Smith, Serial No. 55,262, filed September 9, 1925. Referenceshould now be had to the drawing in which:

Fig. 1 illustrates a preferred embodiment;

Fig. 2 is a modification of the embodiment;

Fig. 3 shows a charactertisic curve having a horizontal portion.

The particular embodiment of the invention illustrated in Fig. 1comprises a transformer l having its primary 2 connected to a source ofalternating current, a rectifier 3, l

which may be of the type disclosed in the aforesaid application,connected to the seca heating element 12. rl`he hollow cathode 11 has arestricted opening 13 inthe end presented to the anodes, andintermediate its ends it has a partition 14 so that the space 15 betweenthe partition 14C and the left-hand end of the cathode constitutes theactive portion, the heating element 12 in the righthand end of thecathode transmitting no electronic current to the anodes but merelyheating the cathode, either during the entire period of operation ormerely while starting. The 'tube preferably contains a readily ionizablegas, such as mercury or csium Vapor, which may for example be at apressure of .01 mm. in the space exterior to the cathode, and, duringoperation, at a higher pressure within the cathode. A rectifier of thisgeneral type is more fully described in the aforesaid application.

rlhe tube 5 may be constructed in a manner similar to the rectifier 3except in that only a single anode 7 isemployed. A. tube of thischaracter has a characteristic curve, such as shown in/Fig. 3, where theabscissee represent current, and the ordinates represent the potentialacross the anode 7 and cathode 8. The reason this tube has acharacteristic of this type is believed to be as follows:

This peculiar characteristic is believed to result from a closerelationship between the internal drop of the tube and the excitation orresonance potential of the gas in the tube (the potential required toput the gas atoms in an excited state). For example, mercury vapor hasan excitation potential of 5.0 volts, although its ionization potential(the potential through which an electron must fall in order to acquiresufficient velocity to ionize lUU a molecule of gas) is 10.6 volts; andwhen the Y atoms are in an excited state it is believed that they can bereadily ionized by succeeding electron impact even although this may beat relatively low velocity. By constructing the tube 5 as describedherein and in the aforesaid application, the internal drop of the tubemay be made to correspond very closely to this excitation potential.While the internal drop may be somewhat higher or somewhat lower thanthe excitation potential it is preferably substantially the same. 'l'.hecharacteristic of the tube chiefly contributing to this condition isbelieved to be the relatively high gas pressure adjacent the activesurface of the cathode which largely if not entirely eliminates theusual potential drop at the cathode. This effect is enhanced by thelocalization of the ionization within the hollow cathode where ionsand/or excited atoms are retained instead of being allowed to escape.The result is that when the tube is thus constructed the current throughthe tube may be varied while maintaining the internal drop substantiallyat the value corresponding to the excitation tential.

The parts a ve described are preferably interconnected as follows: Themidpoint of the secondary 4 is connected through a conductor 16 with thelower side of the load circuit and throu h the branch conductor 17,

with the cath e 8, the anode 7 being connected to the upper side of theload circuit through conductor 18. The opposite ends of the secondary 4are connected to the anodes 9 and 10 of the rectiier 3 throughconductors 19 and 20, respectively. The cathode of the rectifier 3 maybe connected directly to the anode 7 of the device 5 through a conductor21, although this conductor preferably includes an electromagnet 22 forautomatically closing switch 23 in the load circuit when the apparatusis put into operation, the switch 23 being automaticall opened by spring24 when the o ration is 'scontinued It is apparent that y startingtherectiiers with the load circuit open, the initial rush of current andconsequent variation of voltage is minimized.

The heating coils 12 and 12 in the two tubes may be energized in anysuitable manner, as b v windi'n 25 and 26 on transformer 1, the switches27 and 28 being provided to discontinue the energization of theseheaters either durin the operation of the system or at the end o theoperation. Thus, the unidirectional circuit extends from the upper sideof the load circuit 6, through conductor 18, electromagnet 22, conductor21 toV the cathode of the rectifier, and thence alternately, duringalternate half cycles, from the anodes 9 and 10, conductors 19 and 20,secondary 4, and conductor 16 tothe lower side of the load circuit, thetube 5 being connected in parallel with this circuit at points 29 and30.

In operation the unidirectional current in the load circuit tends torise and fall with the alternate half cycles of current delivered by thetransformer 1 but if the parts be properly coordinated with each otherand with the load these variations may be limited to the substantiallyhorizontal portion 31 VV(Fig. 3)

through tube 3 from falling to'zero value between half-cycles andcondensers 34 connected in parallel with the load circuit, switches suchas shown in the drawing being employed if desired to cut these devicesin or out at will. A choke coil 35 may also be employed between the intsof connection of the condensers 34. I 1g. 2 illustrates a modiiicaton ofFig. 1 in which the two tubes 3 and 5 are combined into a single tube 53by making the cathode 54, corresponding to cathode 15 in Fig. 1,function also as an anode for the cathode 55, corresponding to cathode 8in Fig. 1. A Ashield 56 is preferably provided between the cathode andthe anodes 57 and 58, corresponding to the anodes 9 and 10 in 1, toprevent current flowing between the cathode 55 and the anodes.

From the foregoing it will be evident that this invention ischaracterized by the use of thermionic emission in a gaseous medium, incontradistinction to a glow discharge in a gaseous medium, for potentialregulation; the former, unlike the latter, having substantially novoltage drop at the cathode. An-

other unique characteristic consists in the novel relationship betweenthe resonance or excitation potential of the gas and the load potential.

I claim:

1. In combination, a source of alternatin current, a load circuitconnected thereto an normally inoperative, a rectifier inte therebetweenwhereby unidirectional pulsatory current is derived, a device across theload circuit for removing the pulsations and means in series with theload circuit and responsive to rectified current for rendering the loadcircuit operative.

2. An electrical system comprising a source of pulsating current, a loadcircuit connected thereto, means interposed therebetween for smoothingthe pulsating current and means responsive to said current forautomatically closing the load circuit when current flows through saidmeans.

3. electrical system comprising a source -of pulsating current, a loadcircuit connected thereto, a gaseous conduction' regulator interposedtherebetween for smoothing the pulsatmg current and means responsive tosaid current for automatically closing the load circuit when the gaseousmedium in said regulator becomes conducting.

Signed by me at Boston, Massachusetts, this 2nd day of October, 1925.

VANNEVAR BUSH.

